1. Field
A backlight unit is provided.
2. Related Art
Conventionally, cathode ray tubes (CRTs) are mainly used in monitors of TVs, measuring instruments, information terminals, and similar display devices. However, CRTs do not meet the requirements of compact-size and light-weight of electronic products due to their heavy weight and large size.
There is a trend to have smaller and lighter electronic products. CRTs have limitations in reducing their weight and size. Liquid crystal display (LCD) devices utilizing electroluminescent optical effects, plasma display panels (PDPs) using gas discharge, and electroluminescence display (ELD) displays using electroluminescent effects have been used in place of CRTs.
LCD devices have been actively developed as a substitute for CRTs because of the advantages thereof, for example, light-weight, compact-size, and low energy consumption. Recently, LCD devices have been implemented in flat panel display devices, and are most widely used as monitors of desktop computers and large-scale information display devices as well as monitors of laptop computers. Accordingly, the demand for LCD devices is continuously increasing.
Since most LCD devices are light-receiving devices that regulate the intensity of light incident thereto from the outside to display pictures and images, they essentially require the use of additional light sources, namely, backlight units that irradiate light onto LCD panels.
Generally, depending on the arrangement of cylindrical light-emitting lamp(s), backlight units are used as light sources of LCD devices classified into edge-type backlight units and direct-type backlight units.
According to an edge-type backlight unit with a lamp unit arranged at either lateral side of a light guide plate that guides light emerged from the lamp unit. The lamp unit includes a light-emitting lamp, lamp holders inserted in both ends of the lamp to protect the lamp, and a lamp reflection plate wrapped around the lamp, one side of the lamp reflection plate fits to a face of the light guide plate and adapts to reflect the light incident thereto from the lamp toward the light guide plate.
Such an edge-type backlight unit with a lamp unit arranged at either lateral side of a light guide plate is mainly applied to relatively small-sized LCD devices, such as monitors of laptop computers and desktop computers, and has a good light uniformity and long life-span, and is advantageous in achieving thinness of LCD devices.
As the size of LCD devices is increased to 20 inches or above, active developments on direct-type backlight units are being made. According to such a direct-type backlight unit, a plurality of lamps are arranged in a line on a lower surface of a diffusion plate so that light is directly irradiated over the entire surface of an LCD panel.
The direct-type backlight unit has higher light use efficiency than the edge-type backlight unit, and therefore, is mainly employed in large-screen LCD devices that require high brightness.
Since LCD devices that employ the direct-type backlight unit are used in large-sized monitors and television sets, the time of use thereof is longer than laptop computers, and the number of lamps used is greater than that of the edge-type backlight unit. Accordingly, the possibility that the lamps fail and do not turn on due to an exhausted life span is increased in the direct-type backlight unit as compared to the edge-type backlight unit.
Examples of light sources for LCD devices that use the edge-type and direct-type backlight units include electroluminescence (EL) lamps, light-emitting diodes (LEDs), cold cathode fluorescent lamps (CCFLs), hot cathode fluorescent lamp (HCFLs), and external electrode fluorescent lamps (EEFLs).
FIG. 1 is a schematic configuration view that illustrates a conventional edge-type backlight unit.
As shown in FIG. 1, the conventional edge-type backlight unit includes a pair of lamps 10 that serve as light sources that emit light. A light guide plate 11 guides the light incident thereto from the lamps 10 to reflect the light to an LCD panel 14. A diffusion sheet 12 diffuses the light emerged upward from the light guide plate 11 over a predetermined angle. A prism sheet 13 collects the diffused light and transmits the collected light to the LCD panel 14. The LCD panel 14 is arranged on the prism sheet 13. One or more fixing structures (not shown) are arranged below the light guide plate 11. A reflection plate 16 reflects the light being transmitted to the fixing structures to the LCD panel 14 in order to minimize the loss of light.
In addition to the above described configuration, the edge-type backlight unit further includes a lamp reflection plate 18 wrapping around each lamp 10 except for a portion of the lamp 10 facing a light incidence face of the light guide plate 11 in order to reduce the loss of light emerged from the lamp 10 to the light incidence face of the light guide plate 11. A pair of lamp holders 17 are arranged at both ends of the lamp 10 to prevent the light guide plate 11 from coming too close to the lamp 10. A plurality of diffusion sheets 12 may be provided if necessary.
The above described edge-type backlight unit, in which lamps are arranged at opposite sides of a light guide plate, may be used in monitors. Where a single lamp is arranged at only one side of a light guide plate, the backlight unit may be applied to a notebook PC.
As shown in FIG. 2, the conventional direct-type backlight unit for an LCD device includes a plurality of light emitting lamps 1 arranged on a supporting base 2. A rim case 3 is defined along the periphery of the supporting base 2 that fixes the light emitting lamps 1. A plurality of light scattering members 5a, 5b and 5c are arranged between the light emitting lamps 1 and a liquid crystal panel (not shown).
A reflection plate 7 is placed in the rim case 3 on the supporting base 2 that guides light incident thereto from the light emitting lamps 1 to irradiate the light toward a display portion of the liquid crystal panel.
The light emitting lamps 1 are cold cathode fluorescent lamps (CCFLs). In the light emitting lamps 1, electrodes are arranged in a tube at both ends of the tube, and adapted to emit light if power is applied thereto. Both ends of the respective light emitting lamps 1 are fitted into holes perforated through opposite walls of the rim case 3.
Electric power lead lines 9 and 9a are connected to both the electrodes of each light emitting lamp 1 to deliver the power required that drives the light emitting lamp 1. The electric power lead lines 9 and 9a are connected to external connectors that are also connected to a driving circuit. It is necessary to provide the light emitting lamps 1 with the connectors.
The electric power lead line 9 is connected to one of the electrodes of each light emitting lamp 1 and the electric power lead line 9a is connected to the other electrode and they are linked to one connector. One of the electric power lead lines 9 and 9a should be bent to extend below the rim case 3 so as to reach the connector.
The conventional edge-type backlight unit is applicable only to LCDs that have a relatively small scale. The edge-type backlight unit should have a light guide plate that guides light incident thereto from a lamp in an upward direction. The light guide plate is heavy, and thus results in a limit in the manufacture of a light-weight backlight unit.
The direct-type backlight unit has a reflection plate that is arranged beneath light emitting lamps and is insufficient to achieve uniform reflection/diffusion of light emitted from the light emitting lamps, and therefore, is limited in an improvement in uniformity of brightness and use efficiency of light.